In various stages of assembly of large equipment and parts thereof, and particularly for trucks, automobiles, construction machinery, aircraft, or the like, it is generally necessary for workers to place a protective coating on both large and small objects. The large objects present the most difficulty, and such objects are normally coated in an environmentally secure containment structure commonly known as a paint booth. Paint booth structures have been devised and used which effectively employ various air flow design characteristics, to reduce paint booth operating costs while minimizing environmental contamination. In those prior art paint booth designs known to us which achieve both objectives while maintaining adequate paint finish quality, the paint booth operations have resulted in a large quantity of air fillers that are contaminated with paint, and which must be safely and legally handled and discarded. Coating overspray in a typical paint booth might be as much as 50% or more of the volume of coating which adheres to the object being sprayed. With increasingly stringent environmental laws, many paint contaminated filters have had to be handled as hazardous waste, and where such handling is required, a premium has been paid to dispose of the loaded filters in hazardous waste landfills. In particular, the U.S. Environmental Protection Agency, and the environmental agencies in various U.S. states and in other nations, have promulgated regulations and strict standards which require testing and rigorous documentation for land disposal of paint loaded filters which have been produced as a result of paint booth operations.
Collection of overspray paint from a spray booth is generally achieved now by (a) use of paper type filters, (b) use of fiberglass type filters, or (c) use of a water spray curtain for knockout of paint particles to a circulating water bath. Large articles, such as automobiles, are normally painted in a tunnel-type spray booth with the exhaust air and overspray being drawn through a floor grating into a water spray or wet scrubber to remove fine paint droplets. Examples of spray booths of this type are seen in U.S. Pat. Nos. 3,170,384 to Krantz et al.; 3,795,093 to Gerhard et al.; 4,425,870 to Marshke; 4,598,633 to Otto et al.; 4,704,952 to Johnson et al.; 4,759,775 to Patte et al.; 5,040,482 To McGuire et al.; 5,545,239 to Cordier; and 5,676,753 to Josfesson et al. U.S. Pat. No. 5,264,014 to Lannefors et al. shows a similar system in which the wet scrubber is followed by a wet electrostatic precipitator. Smaller articles are usually painted in a cabinet-type spray booth in which air is typically exhausted through the back wall using a bank of dry disposable filters to capture overspray. An example is seen in U.S. Pat. No. 2,583,489 to Meyer. U.S. Pat. No. 2,658,742 shows a catalytic filter for removal of combustible gaseous contaminants. U.S. Pat. No. 3,923,653 to Lavins, Jr. shows a method of removing plastic waste from an extrusion process filter by induction heating.
Both paper and fiberglass filters result in paint saturated filters which must pass a regulatory "paint filter test" that, to pass, must show the absence of free liquids, before disposal in a landfill is allowed. Typically, such filters must be disposed, at relatively high cost, in a hazardous waste landfill. Also, wet spray booth designs generally result in the creation of significant quantities of sludge, which must be periodically removed from the treatment system and disposed, often by shipment to a hazardous waste landfill.
In spite of the various schemes which have so far been offered to the marketplace to reduce airflow, limit overspray, or to enhance paint filter life, a continuing and growing demand exists for a simple and inexpensive apparatus and method which can be used to preserve and enhance the life cycle of paint filters, thus reducing overall costs. The need for improved filters and for improved methods for paint booth construction and operation is especially acute in conjunction with new fabrication or refurbishment work where large mobile objects are to be painted, such as heavy haul trucks, rail cars, construction machinery, or large commercial aircraft. As will be evident to those familiar with such paint booths and to whom this specification is particularly addressed, a novel downdraft paint booth floor construction and filter apparatus, and a method of using the filter apparatus which effectively eliminates the necessity of disposing of large quantities of spent paint filters, would be of great benefit in increasing the profitability of manufacturing plants.